Study on molecular structure and vibrational spectra of 5,7-dimethoxycoumarin using DFT: A combined experimental and quantum chemical approach

Conformational analysis of 5,7-Dimethoxycoumarin was performed and two stable conformers were obtained. The difference between the total energies of these conformers was 1.4698 kcal/mol and the difference between the zero point corrected energies was nearly zero. Vibrational frequencies of these conformers were calculated by B3LYP method using 6-311++G(d, p) basis sets and compared with experimentally recorded FT-IR and Raman spectra. Vibrational assignments were made by calculated total energy distributions. Time dependent density functional theory calculations were done by the same level of theory in order to investigate low-lying excited state and obtained results were compared with the maximum absorbtion peak value of experimental UV-visible spectrum.